1. Field of the Invention
The present invention relates to an adaptive controller for cyclic signal, which a vibration generation source generates. The adaptive controller actively removes the influences of cyclic signal, which the cyclic signal exerts to an objective evaluation point, by adding an adaptive signal, which synchronizes with the cyclic signal, to the cyclic signal. Thus, the adaptive controller reduces vibration actively at the objective evaluation point.
2. Description of the Related Art
JP-A-2005-309,662, for instance, discloses a conventional adaptive controller. The patent publication sets forth to make a differential computed value zero. The differential computed value herein is produced by adding an adaptive signal to a signal, which a vibration generation source generates.
When one and only transfer path is present from a vibration generation source to an objective evaluation point, such a conventional adaptive controller, which makes a differential computed value zero, can surely make a vibration at the objective observation point zero.
However, when a plurality of transfer paths are present from a vibration generation to an objective evaluation point, the following problems arise if the conventional adaptive controller is applied to control a vibration, which occurs in one of the transfer paths.
Firstly, suppose that no adaptive control is applied to a plurality of transfer paths, vibrations, which are transferred by way of a plurality of transfer paths, cancel with each other so that a vibration at an objective evaluation might be reduced consequently. In such a situation, when the conventional adaptive controller is applied to one of the transfer paths, a vibration, which occurs in one of the transfer paths, is reduced, and accordingly does not act to cancel vibrations, which occur in the other transfer paths. As a result, there is a fear that a vibration at an objective evaluation might be enlarged adversely.
Secondly, vibrations, which are transferred by way of a plurality of transfer paths, might often exhibit different proportions of contribution to an objective evaluation point for every frequency, respectively. For example, when the conventional adaptive controller is applied to one of the transfer paths, it is possible to reduce a vibration at an objective evaluation point if a vibration, which occurs in the one of the transfer paths, contributes greatly to canceling the frequency of a vibration at an objective evaluation point. However, in the other frequency bands, even if the conventional adaptive controller is applied to one of the transfer paths, it might not be possible to reduce a vibration at an objective evaluation point so much. In this instance, since the reduction magnitude of vibrations differ for every frequency, the changing proportion of vibration might enlarge with respect to the change of frequency. That is, the gap between the crests and roots of vibration might enlarge. Such a change might give unpleasant feelings to certain people.
Moreover, it has been attracting engineers' attention to make tones by utilizing vibrations and/or noises. However, when the conventional adaptive controller is applied to the making of tunes, it is necessary to generate vibration anew in making tunes because the conventional adaptive controller operates to make vibrations and/or noises zero at an objective evaluation point. Consequently, such a tune making is very poor in terms of the energy efficiency.